Two-component silicone compositions have been known and are used as adhesives and sealants in different applications. Compared to compositions with silane-cross-linking organic polymers (carbon-based polymer skeleton), such as, for example, silane-terminated polyurethanes, silicone compositions have a considerably higher UV stability; they are thereby suitable for applications where the adhesion or sealing is exposed to at least partial solar radiation.
Two-component silicone compositions that cross-link at room temperature, also known as RTV-2 silicones (RTV-2: “room temperature vulcanizing, 2-part silicones”), are known.
For example, such a two-component silicone composition is described in EP 0 787 766 A1. So as not to impair the shelf life of the composition or to prevent premature, accidental curing, the main components, namely an α,ω-dihydroxypolydiorganosiloxane and a catalyst for the cross-linking of polydiorganosiloxanes, are stored in two separate components. In the application of such a composition, the two components are then mixed together, whereupon the cross-linking or the curing of the composition results.
Such two-component silicone compositions described in EP 0 787 766 A1 can lead to the so-called mixer open time problem. The latter primarily arises when the two components are mixed together via a static mixer or the like. In this case, namely during the meeting of the two components upon entry into the static mixer, the result can be a brief, local overconcentration of the catalyst-containing component relative to the polydiorganosiloxane-containing component, which can lead to quick curing of the composition inside the static mixer and can clog the latter. This occurs if the polydiorganosiloxane-containing component compared to the catalyst-containing component is used in a ratio by weight of ≧1:1, which is often the case in practice.
Possibilities for addressing the so-called mixer open time problem include, for example, the reduction of the catalyst concentration in the catalyst component, either by actual reduction of the catalyst content or else by higher dilution of the catalyst. The reduction of the catalyst content can result in an increase of the curing period, i.e., the pot life, which can be undesirable. It can entail higher dilution of the catalyst, such that additional diluents have to be used or non-reactive integral parts from the polydiorganosiloxane-containing component have to be shifted to the catalyst component, which can entail impairments in the workability and/or in the mechanics of the cured composition, and can limit the possibilities of the configuration of the composition.
The use of the catalyst in the polydiorganosiloxane-containing component has proved unsuitable to date for reasons of the shelf life of the silicone composition.